1. Field of the Invention
The present invention relates to a rotary speed controller for controlling the rotating speed and a rotary controlling phase of a rotary machine by using a monostable circuit as a synchronous pull-in means for obtaining a DC voltage responsive to the rotating speed of the rotary machine. Tracking of synchronous pull-in conditions is satisfactorily achieved for change-over from one speed to another or for fine control of the rotating speed of the rotary machine, by changing the astable period of a monostable circuit responsive to the change of a reference frequency for speed change-over or to the fine frequency control of a reference signal source.
Prior Art
As for a conventional apparatus, for example, to control the rotation speed of the turntable of a record player precisely, it requires phase comparison means which compares a reference frequency signal obtained from a reference frequency oscillator using a solid vibrator such as a crystal vibrator with the output signal from the rotating speed detector (such as frequency generator) connected with said turntable.
Synchronous pull-in means is also necessary, which draws the rotating speed of said turntable to the setting value, to make said phase comparison in a satisfactory condition.
As for said synchronous pull-in means, the output signal of said rotating speed detector is transformed to the signal, whose average level changes in accordance with the rotating speed of said turntable. As a most general example, the output signal of said rotating speed detector is applied to a monostable circuit, and DC voltage, which changes in accordance with the rotating speed of said turntable, is usually obtained, by smoothing output signals of said monostable circuit by an integration circuit. Two standard rotating speeds of record player are 331/3rpm and 45 rpm; in some cases the precise control within several % is often requested for both rotating speeds. Among change-over methods of the rotating speed, prior art method is varying said reference frequency of the apparatus or changing-over, which requires to reset the astable period of said monostable circuit, since the synchronous pull-in condition changes.
Therefore, in the conventional method, one changes the resistors which set astable period of said monostable circuit in accordance with the change-over of reference frequency. However, in this method, more than two switch circuits are required, and this leads to the complication of the structure of the apparatus and the wiring. When one needs the precise control of the rotating speed, it needs to control the reference frequency precisely, sacrificing synchronous drawing characteristics, or alternatively, it needs to employ the precise control mechanism of astable period which is related to control mechanism of reference frequency.